Nguyen M H, Harbour D, Gagnon C
J Neurochem. 1987 Jul;49(1):38-44. doi: 10.1111/j.1471-4159.1987.tb03391.x.
The carboxyl methylation of secretory proteins in vivo was investigated in bovine adrenal medullary cells in culture. Chromogranin A, the major intragranular secretory protein in adrenal medullary cells, and other secretory proteins were found to be carboxyl-methylated within secretory vesicles. The in vivo labeling pattern using [methyl-3H]methionine and the in vitro labeling pattern using S-adenosyl-[methyl-14C]methionine of intravesicular secretory proteins were similar. The detection of methylated chromogranin A in mature secretory vesicles required 3-6 h, a time consistent with the synthesis and storage of secretory proteins in this tissue. Carboxyl-methylated chromogranin A was secreted from medullary cells by exocytosis via activation of nicotinic cholinergic receptor and recovered still under the methylated form in the incubation medium. Since protein-carboxyl-methylase is cytosolic, these results suggest that methylation of secretory proteins is a cotranslational phenomenon.
在培养的牛肾上腺髓质细胞中研究了体内分泌蛋白的羧基甲基化。嗜铬粒蛋白A是肾上腺髓质细胞中主要的颗粒内分泌蛋白，发现其他分泌蛋白在分泌小泡内被羧基甲基化。使用[甲基-3H]甲硫氨酸的体内标记模式和使用S-腺苷-[甲基-14C]甲硫氨酸的小泡内分泌蛋白的体外标记模式相似。在成熟分泌小泡中检测甲基化的嗜铬粒蛋白A需要3-6小时，这与该组织中分泌蛋白的合成和储存时间一致。羧基甲基化的嗜铬粒蛋白A通过烟碱胆碱能受体的激活经胞吐作用从髓质细胞分泌出来，并在孵育培养基中仍以甲基化形式回收。由于蛋白质羧基甲基转移酶是胞质的，这些结果表明分泌蛋白的甲基化是一种共翻译现象。
